The present invention relates to an angular position sensor for use with a vehicle steering column assembly, and more particularly, an angular position sensor capable of providing a digital electronic signal representative of the absolute position of a steering wheel that utilizes error correction features.
Various types of angular position sensors are currently used in conjunction with vehicle steering wheels, or hand wheels, including relative, absolute, analog and digital angular position sensors. A relative angular position sensor measures the angular position of a rotating object by either incrementing or decrementing a counter, depending upon the rotational direction of the object, and relating that information to an angular reference point. A sensor of this type has the advantage of being able to operate with minimum complexity. For instance, a relative angular position sensor can determine the rotational position of a steering wheel by using a data wheel having only two bits, or xe2x80x9ctracksxe2x80x9d, of information. On the other hand, this type of sensor has the disadvantage of being unable to independently determine the angular position of an object at any one moment. Stated differently, this type of sensor requires an angular reference point, or starting point. Rotational movement away from this point causes the sensor to either increment or decrement a counter, depending upon the direction of rotation. If the object is rotated too quickly or there is a damaged track such that an increment or decrement is missed, then all subsequent angular position readings will be incorrect. Furthermore, if power to the sensor is ever interrupted such that the information in the counter is lost, then the sensor will have to utilize a reset or reference type feature to begin again.
Conversely, an absolute angular position sensor uses a unique position identifier for each angular position, thus, it is capable of measuring the angular position of a steering wheel independently of an angular reference point. This type of position sensor divides the total possible angular extent of the steering wheel""s rotation (typically 1800xc2x0) into angular positions. Each position is assigned a unique position identifier, which is typically represented as a combination of binary data bits. If a greater resolution is required, then the number of positions, and hence data bits, is increased, thus decreasing the angular extent of each of the positions. For example, if an absolute angular position sensor for a steering wheel must have a resolution of 0.5, then at least 12 bits of information are required ((1800/212) less than 0.5). There are various techniques for determining the absolute angular position of a rotatable object, some of those techniques are disclosed in U.S. Pat. Nos. 6,240,652, 6,248,993 and 6,304,190, each of which teaches an absolute angular position sensor for use with a vehicle steering wheel.
Traditionally, most absolute angular position sensors were analog sensors. These types of sensors have certain advantages over their relative position sensing counterparts, and often times utilize Hall Effect or magnetoresistor-type electrical components. An example of an analog absolute angular position sensor is seen in U.S. Pat. No. 6,400,142, which is assigned to the present assignee, Delphi Technologies, Inc. Though, use of this type of sensor is advantageous in many scenarios, certain applications require higher levels of resolution and error correction features to protect against corrupted data. One way to achieve these requirements is through the use of digital sensors.
Digital angular position sensors, while capable of high levels of resolution and error correction, typically measure on object""s relative angular position as opposed to its absolute angular position. As previously indicated, relative angular position sensors generally utilize some type of counter and angular reference point, and suffer from certain drawbacks associated therewith. A digital relative angular position sensor could provide a signal where the most significant bits of information indicate the relative angular position, and the least significant bits provide an error correction code.
Thus, it would be advantageous to provide an angular position sensor for use with a vehicle steering wheel, where the sensor enjoys certain advantages associated with absolute and digital angular position sensors, yet avoids certain drawbacks found in relative and analog angular position sensors.
The above-noted shortcomings of prior art angular position sensors are overcome by the present invention which provides an angular position sensor assembly for use with a vehicle steering column assembly that comprises a digitally encoded disk, an optical output device, an optical input device and a signal output. The encoded disk includes both absolute angular position bits and error correction bits, which may be used by the optical output and input devices to provide an angular position signal that is representative of both the absolute angular position information and error correction information.
According to another embodiment, the present invention provides an angular position sensor assembly similar to that just described, however, this sensor assembly includes an encoded disk also having Reed-Solomon error correction bits and data words that include both angular position information and error correction information.
According to yet another embodiment, the present invention provides a method for determining the absolute angular position of a vehicle steering wheel. This method includes the steps of providing a digitally encoded disk, an optical output device, an optical input device, and a signal output, all of which are similar to those previously mentioned. The method also includes steps related to the emission and reception of light through the encoded disk, as well as generating an angular position signal representative of both absolute angular position information and error correction information.
Objects, features and advantages of this invention include, but are not limited to, providing an improved angular position sensor assembly that is digital, determines the absolute angular position of a steering wheel, and includes error correction features.